Question: Multiply.
Explanation: $2{,}478 \times 5$ and $24.78\times 0.05$ multiply the same digits in the same order. So, the product of both problems will also have the same digits in the same order. Let's multiply $2{,}478 \times 5$. Then we can estimate to place the decimal point in the product of $24.78 \times 0.05$. $\begin{aligned} 2{,}478&\\ \underline{ \times 5}&\\ 40}& {5} \times {8\text{ ones}}\\ 350}& {5} \times{7\text{ tens}}\\ 2{,}000}& {5} \times {4\text{ hundreds}}\\ \underline{+10{,}000}}& {5} \times {2\text{ thousands}}\\ 12{,}390 \end{aligned}$ $2{,}478 \times 5 = 12{,}390$ Let's estimate to place the decimal in $24.78 \times 0.05$. $\begin{aligned} 24.78 \times 0.05 &\approx 20\times 0.1\\\\ &\approx 2 \end{aligned}$ Where can we place the decimal in $12{,}390$ to get a product close to $2$ ? $1.239 = 24.78 \times 0.05$